Factors Associated with Duck Nest Success
in the Prairie Pothole Region of Canada

Causes of Nest Failure

The high rate of nest failure due to depredation of clutches that we observed
is consistent with other recent investigations in the PPR (Higgins 1977, Cowardin
et al. 1985, Greenwood 1986, Johnson et al. 1987, Klett et al. 1988). Besides
nests that failed directly because of predation on eggs, we believe many nests
that were abandoned without evidence of egg destruction also failed because predators,
especially raptors, killed attending females; this is indicated by our finding
of female carcasses at 11% of 190 nests abandoned without evidence of egg destruction
(See Mortality of Adults). Large raptors are known to prey on adult ducks
(McInvaille and Keith 1974, Schmutz et al. 1980), but few raptors that eat eggs
were present on our study areas (Sargeant et al. 1993). An exception is the northern
harrier, which occasionally preys on hatching eggs (Willms and Kreil 1984).

Farming activities were not a major source of nest failure except for northern
pintails; few other species nested in Cropland and there were few nests in Hayland.
We did not observe nest destruction in Right-of-way and dry Wetland by mowing
that occurred on most study areas in late June. Had our study been conducted
during wetter years more favorable to renesting, we might have found mowing
to be a greater cause of nest failure. Mowing has been shown to cause much nest
destruction and female mortality in other studies (Ordal 1964, Evans and Wolfe
1967, Cowardin et al. 1985).

Weather events, likewise, were not a major cause of nest failure, although
storms were important locally. Snowstorms caused embryo mortality and nest abandonment,
especially among mallards and northern pintails. Although embryos can survive
limited exposure to subfreezing temperatures (Greenwood 1969, Batt and Cornwell
1972), Dzubin and Gollop (1972) reported that chilling of embryos during cold
spring weather was partly responsible for failure of up to 9% of eggs in early
mallard nests. Johnson et al. (1986) suggested that nest failure due to spring
snowstorms may be compensated by renesting due to improved wetland conditions.
Storms also may benefit nesting ducks by delaying cultivation, but Milonski
(1958) and Krapu (1977) speculated that ducks might not benefit if such delay
only postpones nest destruction until a later date when conditions may be less
favorable for renesting. Reduced availability of aquatic invertebrates that
are consumed by laying females also may occur after snowstorms and influence
nesting (Krapu 1979, Swanson et al. 1979). Dane and Pearson (1971) reported
that mallards and northern pintails ceased laying during a severe spring snowstorm.

Flooding destroyed duck nests on the Hay Lakes and Holden study areas in 1983
but was of little consequence elsewhere. Flooding on these study areas was aggravated
by drainage; ditches that connected wetlands appeared to accelerate movement
of run-off water among basins and cause low-lying areas to flood rapidly. Johnson
et al. (1986) suggested that flooding in mid-May should have only minor influence
on mallards because renesting would compensate for losses. We found that flooding
in June, however, caused the failure of nearly 50% of the nests of mallards
that were probably renesting, and also numerous nests of late-nesting species
such as the lesser scaup and ruddy duck, which are not prone to renest (Bellrose
1980).